A cataract was a speed control device used in early single-acting rocker steam engines, particularly atmospheric engines and Cornish engines. It is clearly different from the centrifugal governor, as it does not control the stroke speed of the engine, but rather the time between strokes.
Operation
The typical installation of a beam engine built in a "engine house" spanned four floors. The cylinder and the usual working position of the engine operator were located in the 'lower chamber', approximately at ground level. Above it was the 'middle chamber', with the upper cylinder cover and 'upper nozzle' (the upper valve housing), and above it was the 'upper chamber' or beam beam chamber.[3] The falls were placed at the lowest part. of the engine box, in a chamber located below the lower chamber, together with the exhaust pipe. This space was difficult to access, and was not visited during normal operation.
The valve gear "Timing mechanism (steam engine)") (or 'working gear') of a Newcomen or Cornish engine is based on a connecting rod. It is a vertical bar, hanging from the beam, and moving parallel to the piston. Adjustable tappets are attached to this rod. These tappets strike long curved iron levers ('horns') connected to three horizontal shafts or 'arbors'.[note 1] Each shaft operates one of the engine's valves. For Cornish cycles, these valves are the upper steam inlet to the top of the cylinder, the balance valve joining the upper and lower parts of the cylinder, and the lower exhaust and condensate water injection valves, which share a shaft. Unlike most other steam engines, these engines can run intermittently: making a single stroke before stopping and waiting for the valves to reset again. The speed of each power stroke or 'input' 'inboard' was a characteristic of the engine and was not easily varied, but it was not necessary for the engines to run continuously, stroke after stroke.[6] This was in direct contrast to the rotary arm engine and the rotary nature of almost all other steam engines. With the original Newcomen cycle, the speed of the return stroke varied according to the boiler pressure, although this still did not affect the force or speed of the thrust stroke.[7].
The use of a cataract could allow an engine to run at only one-third of its free speed.[8] When the pumping load was variable, the cataracts could also be connected and disconnected as necessary, allowing the engine to run at full speed for a period and then stop thereafter.[9].
Speed regulating dampers
Introduction
A cataract was a speed control device used in early single-acting rocker steam engines, particularly atmospheric engines and Cornish engines. It is clearly different from the centrifugal governor, as it does not control the stroke speed of the engine, but rather the time between strokes.
Operation
The typical installation of a beam engine built in a "engine house" spanned four floors. The cylinder and the usual working position of the engine operator were located in the 'lower chamber', approximately at ground level. Above it was the 'middle chamber', with the upper cylinder cover and 'upper nozzle' (the upper valve housing), and above it was the 'upper chamber' or beam beam chamber.[3] The falls were placed at the lowest part. of the engine box, in a chamber located below the lower chamber, together with the exhaust pipe. This space was difficult to access, and was not visited during normal operation.
The valve gear "Timing mechanism (steam engine)") (or 'working gear') of a Newcomen or Cornish engine is based on a connecting rod. It is a vertical bar, hanging from the beam, and moving parallel to the piston. Adjustable tappets are attached to this rod. These tappets strike long curved iron levers ('horns') connected to three horizontal shafts or 'arbors'.[note 1] Each shaft operates one of the engine's valves. For Cornish cycles, these valves are the upper steam inlet to the top of the cylinder, the balance valve joining the upper and lower parts of the cylinder, and the lower exhaust and condensate water injection valves, which share a shaft. Unlike most other steam engines, these engines can run intermittently: making a single stroke before stopping and waiting for the valves to reset again. The speed of each power stroke or 'input' 'inboard' was a characteristic of the engine and was not easily varied, but it was not necessary for the engines to run continuously, stroke after stroke.[6] This was in direct contrast to the rotary arm engine and the rotary nature of almost all other steam engines. With the original Newcomen cycle, the speed of the return stroke varied according to the boiler pressure, although this still did not affect the force or speed of the thrust stroke.[7].
The waterfall itself resembled a small plunger pump. It was an iron box in a cistern filled with water, with a plunger or piston placed on top and pressed down by a weight. The water inside the pump could only escape through a small tap or valve.[10][11] As the plunger gradually fell, its motion was passed upward (by a swinging lever and rod) to the valve device in the central chamber. Once the rod had been raised sufficiently, the first valve was opened to admit steam into the top of the cylinder, beginning a new stroke.[note 2].
Once the expansive stroke began, the motor pushed down on the cataract rocker lever. This raised the plunger, which acted as a suction pump inside the cataract to refill the plunger, through a flap valve from its surrounding cistern.[13] The cistern was kept full of water thanks to the pump that the engine was driving.
The water outlet valve was controlled by a rod from the lower chamber, used by the engine operator to control the operating speed, according to the work required.[13].
The cataract actuating rod also had a screw adjuster, which acted to vary the water injection time (Newcomen) or the phase between the inlet and exhaust valves (Cornwall).[13] This could be used to provide a longer, more effective condensation time, if the condensation water supply was somewhat warmer, such as in the summer. However, this adjustment appears to have been little understood and little used by engine operators.[10].
Development
first waterfalls
The cataract first appeared on Newcomen engines in Cornwall, although its inventor is unknown. They were known in Smeaton's time, and may be another of the developments in the Newcomen engine for which he was responsible.[6] James Watt found them on his trip to Cornwall in 1777.[14] They were of a simpler type: called 'jack in the box', they consisted of a simple wooden box swiveling on a pivot, filled with water through an adjustable wrench. When the box was filled enough to unbalance a lever, the engine's injection valve was activated.
watt
Boulton and Watt used the simple overturned box waterfall design for some years, until around 1779. After this, other designs were used, including a water waterfall where the same water was used and continuously recycled and also an air system using a circular bellows. A cataract of this type was supplied for the Ale and Cakes mine.") The design of the cataract plunger pump had appeared in Cornwall in 1785, but was not Watt's invention.
Posterior cataracts
The term 'cataract' became synonymous with damping cylinder"), at least when associated with steam engines and their regulating systems. They were used as a damping device to prevent excessive sensitivity with respect to centrifugal regulators.[17].
Cataracts were also used as a safety device to prevent excessive speeds in direct-acting water pumps.[note 3] A rocker lever or 'differential' was placed between the pump's piston rod and a cataract set to the normal working speed of the pump. If the pump suddenly accelerated, due to pump collapse or some similar problem, the piston would reach cataract and the action of the differential lever would close the pump's steam inlet valve and stop it, limiting possible damage to the engine.[18].
Open loop control
Contenido
La catarata, como la mayoría de los reguladores, es un ejemplo de servomecanismo. Sin embargo, a diferencia del más conocido regulador centrífugo de Watt, este es un control de circuito abierto, en lugar de un control de circuito cerrado. La catarata funciona a su propia velocidad, pero no mide la velocidad resultante del motor. También se ha descrito como un "reloj de agua".[15] Esto supone que la relación entre el funcionamiento de la catarata y la velocidad del motor es fija, una suposición válida para un motor de balancín ya que la catarata controla la sincronización de la carrera del motor, en lugar de una válvula de potencia o acelerador variable. Cuando un regulador controla una válvula de mariposa de este tipo, como el regulador de Watt, la velocidad del motor depende de una relación compleja e impredecible entre la carga del motor, la posición de la válvula y la eficiencia variable del motor. Dichos reguladores deben usar un control de circuito cerrado para mantener un control efectivo y preciso.
Synchronization
An advantage of the open-loop, independent nature of the cataract control was that two motors could be set to operate in synchronization, but in antiphase ("Phase (wave)"). With pumping motors, this gave a more uniform output to their pumping.[19].
Centrifugal regulator
Although the centrifugal governor was already known from its use for water and windmills, it was not until 1788 that Watt was the first to apply it to a steam engine.[20] This was the 'Lap Engine', an early rotary engine now preserved in the Science Museum, London.
With a rotary engine, it was necessary to control the speed at which the cylinder moved throughout its stroke, not just to vary the time between strokes. This required the use of a butterfly valve on the steam supply, controlled by the regulator. As the load on industrial engines and similar uses could vary, closed-loop control was also needed, such as the centrifugal governor based on engine speed.[20] Cataract was therefore not used on rotary engines, even where single-acting Cornish winding motors were still used in their place of origin.[21]
The Cornish engines could not be controlled by a throttle valve, as their operating cycle depended more on condensation time than on control of the steam supply. Non-rotary rocker arm engines also had no easy means of including a centrifugal governor. For these reasons, the cataract remained in service for as long as the Cornish Engine did.[22].
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[4] ↑ Algunos motores de bobinado de Cornualles tenían sus válvulas dispuestas en diferentes números de cenadores, aunque su funcionamiento básico sigue siendo el mismo.
[14] ↑ Este es el inicio de una carrera en el ciclo de Cornualles. Para un motor Newcomen, la catarata activaba la válvula de inyección de agua que causaba la condensación en el cilindro,[12] y por lo tanto el inicio del ciclo de empuje.
[20] ↑ Estos eran el tipo de bomba recíproca pequeña, comúnmente utilizada como bomba de agua de alimentación de la caldera, a menudo descrita como del tipo 'Weir'.
The use of a cataract could allow an engine to run at only one-third of its free speed.[8] When the pumping load was variable, the cataracts could also be connected and disconnected as necessary, allowing the engine to run at full speed for a period and then stop thereafter.[9].
The waterfall itself resembled a small plunger pump. It was an iron box in a cistern filled with water, with a plunger or piston placed on top and pressed down by a weight. The water inside the pump could only escape through a small tap or valve.[10][11] As the plunger gradually fell, its motion was passed upward (by a swinging lever and rod) to the valve device in the central chamber. Once the rod had been raised sufficiently, the first valve was opened to admit steam into the top of the cylinder, beginning a new stroke.[note 2].
Once the expansive stroke began, the motor pushed down on the cataract rocker lever. This raised the plunger, which acted as a suction pump inside the cataract to refill the plunger, through a flap valve from its surrounding cistern.[13] The cistern was kept full of water thanks to the pump that the engine was driving.
The water outlet valve was controlled by a rod from the lower chamber, used by the engine operator to control the operating speed, according to the work required.[13].
The cataract actuating rod also had a screw adjuster, which acted to vary the water injection time (Newcomen) or the phase between the inlet and exhaust valves (Cornwall).[13] This could be used to provide a longer, more effective condensation time, if the condensation water supply was somewhat warmer, such as in the summer. However, this adjustment appears to have been little understood and little used by engine operators.[10].
Development
first waterfalls
The cataract first appeared on Newcomen engines in Cornwall, although its inventor is unknown. They were known in Smeaton's time, and may be another of the developments in the Newcomen engine for which he was responsible.[6] James Watt found them on his trip to Cornwall in 1777.[14] They were of a simpler type: called 'jack in the box', they consisted of a simple wooden box swiveling on a pivot, filled with water through an adjustable wrench. When the box was filled enough to unbalance a lever, the engine's injection valve was activated.
watt
Boulton and Watt used the simple overturned box waterfall design for some years, until around 1779. After this, other designs were used, including a water waterfall where the same water was used and continuously recycled and also an air system using a circular bellows. A cataract of this type was supplied for the Ale and Cakes mine.") The design of the cataract plunger pump had appeared in Cornwall in 1785, but was not Watt's invention.
Posterior cataracts
The term 'cataract' became synonymous with damping cylinder"), at least when associated with steam engines and their regulating systems. They were used as a damping device to prevent excessive sensitivity with respect to centrifugal regulators.[17].
Cataracts were also used as a safety device to prevent excessive speeds in direct-acting water pumps.[note 3] A rocker lever or 'differential' was placed between the pump's piston rod and a cataract set to the normal working speed of the pump. If the pump suddenly accelerated, due to pump collapse or some similar problem, the piston would reach cataract and the action of the differential lever would close the pump's steam inlet valve and stop it, limiting possible damage to the engine.[18].
Open loop control
Contenido
La catarata, como la mayoría de los reguladores, es un ejemplo de servomecanismo. Sin embargo, a diferencia del más conocido regulador centrífugo de Watt, este es un control de circuito abierto, en lugar de un control de circuito cerrado. La catarata funciona a su propia velocidad, pero no mide la velocidad resultante del motor. También se ha descrito como un "reloj de agua".[15] Esto supone que la relación entre el funcionamiento de la catarata y la velocidad del motor es fija, una suposición válida para un motor de balancín ya que la catarata controla la sincronización de la carrera del motor, en lugar de una válvula de potencia o acelerador variable. Cuando un regulador controla una válvula de mariposa de este tipo, como el regulador de Watt, la velocidad del motor depende de una relación compleja e impredecible entre la carga del motor, la posición de la válvula y la eficiencia variable del motor. Dichos reguladores deben usar un control de circuito cerrado para mantener un control efectivo y preciso.
Synchronization
An advantage of the open-loop, independent nature of the cataract control was that two motors could be set to operate in synchronization, but in antiphase ("Phase (wave)"). With pumping motors, this gave a more uniform output to their pumping.[19].
Centrifugal regulator
Although the centrifugal governor was already known from its use for water and windmills, it was not until 1788 that Watt was the first to apply it to a steam engine.[20] This was the 'Lap Engine', an early rotary engine now preserved in the Science Museum, London.
With a rotary engine, it was necessary to control the speed at which the cylinder moved throughout its stroke, not just to vary the time between strokes. This required the use of a butterfly valve on the steam supply, controlled by the regulator. As the load on industrial engines and similar uses could vary, closed-loop control was also needed, such as the centrifugal governor based on engine speed.[20] Cataract was therefore not used on rotary engines, even where single-acting Cornish winding motors were still used in their place of origin.[21]
The Cornish engines could not be controlled by a throttle valve, as their operating cycle depended more on condensation time than on control of the steam supply. Non-rotary rocker arm engines also had no easy means of including a centrifugal governor. For these reasons, the cataract remained in service for as long as the Cornish Engine did.[22].
Find more "Speed regulating dampers" in the following countries:
[4] ↑ Algunos motores de bobinado de Cornualles tenían sus válvulas dispuestas en diferentes números de cenadores, aunque su funcionamiento básico sigue siendo el mismo.
[14] ↑ Este es el inicio de una carrera en el ciclo de Cornualles. Para un motor Newcomen, la catarata activaba la válvula de inyección de agua que causaba la condensación en el cilindro,[12] y por lo tanto el inicio del ciclo de empuje.
[20] ↑ Estos eran el tipo de bomba recíproca pequeña, comúnmente utilizada como bomba de agua de alimentación de la caldera, a menudo descrita como del tipo 'Weir'.